Electromigration (EM) is the transport of atoms within a conductive material, which is caused by collisions that transfer momentum between conducting electrons and the atoms of the conductive material. Modern day integrated chips often experience electromigration in metal interconnect layers. For example, as electrons carry a current to a semiconductor device, the electrons collide with metal atoms in the metal interconnect layers. The collisions cause metal atoms within the metal interconnect layers to move (i.e., undergo electromigration), resulting in voids in the metal interconnect layers that can lead to integrated chip (IC) failure.
Traditional EM analysis has focused on higher metal layers that interconnect the cells. With shrinking wire dimensions and increasing current density, the current in lower metal layers within the cells may induce EM phenomenon on the lower metal lines. However, during the signal EM signoff flow, the traditional tools may not be able to check the EM condition on the cell output pins.